The present invention generally relates to the construction of vacuum processing chambers used for processing substrates, and more specifically to techniques for variable seal pressure slit valve doors.
In general, vacuum processing chambers for processing substrates include a substrate transfer opening, commonly known as a slit valve. A slit opening, a tunnel-like passage associated with the slit valve, is used to transfer substrates between a process chamber, also called a reactor chamber, and a transfer chamber. The slit valve opening is commonly sealed at an outside surface of the process chamber body by a blocking plate which moves over the slit valve opening. This blocking plate is a conventional slit valve door. A perfluoro elastomeric o-ring is generally attached to the conventional slit valve door to provide a seal.
During processing, a high slit valve door sealing pressure is applied, typically about 80 psi to 90 psi, due to a large pressure gradient between the process and transfer chambers. High pressure, in the range of about 10 to 760 torr, is often used in a process chamber to enhance the process being performed, such as during wafer film deposition. Meanwhile, the transfer chamber is usually kept at 0.3 torr. The high sealing pressure introduces a tensile stress on the exposed surface of the tightly compressed o-ring.
During a chamber cleaning process, the process chamber is usually at a much lower pressure, in the range of about 1 to 4 torr. The slit door, including the o-ring, is exposed to cleaning gases. These cleaning gases, such as fluorine, attack the chemical composition of the o-ring causing the formation of particle contaminants. These particles can contaminate the process chamber and damage substrates.
Until now there has been no satisfactory solution to overcome o-ring contaminants for a slit valve door due to chemical attack, in that conventional vacuum processing chambers are constructed in a configuration that gives rise to particles from 0-rings in the process chamber.